Journal of Vacuum Science & Technology B emphasizes processing, measurement and phenomena associated with micrometer and nanometer structures and devices. Processing may include vacuum processing, plasma processing and microlithography among others, while measurement refers to a wide range of materials and device characterization methods for understanding the physics and chemistry of submicron and nanometer structures and devices.

The authors study the electrical transport properties of atomically thin individual crystalline grains of MoS2 with four-probe scanning tunneling microscopy. The monolayer MoS2 domains are synthesized by chemical vapor deposition on SiO2/Si substrate. Temperature dependent measurements on conductance and mobility show that transport is dominated by an electron charge trapping and thermal release process with very low carrier density and mobility. The effects of electronic irradiation are examined by exposing the film to electron beam in the scanning electron microscope in an ultrahigh vacuum environment. The irradiation process is found to significantly affect the mobility and the carrier density of the material, with the conductance showing a peculiar time-dependent relaxation behavior. It is suggested that the presence of defects in active MoS2 layer and dielectric layer create charge trapping sites, and a multiple trapping and thermal release process dictates the transport and mobility characteristics. The electron beamirradiation promotes the formation of defects and impact the electrical properties of MoS2. Our study reveals the important roles of defects and the electron beamirradiation effects in the electronic properties of atomic layers of MoS2.

The most direct definition of a patterning process' resolution is the smallest half-pitch feature that is capable of transferring onto the substrate. Here, the authors demonstrate that thermal scanning probe lithography (t-SPL) is capable of fabricating dense line patterns in silicon and metal lift-off features at sub-20 nm feature size. The dense silicon lines were written at a half pitch of 18.3 nm to a depth of 5 nm into a 9 nm polyphthalaldehyde thermal imaging layer by t-SPL. For processing, the authors used a three-layer stack comprising an evaporated SiO2 hardmask, which is just 2–3 nm thick. The hardmask is used to amplify the pattern into a 50 nm thick polymeric transfer layer. The transfer layer subsequently serves as an etch mask for transfer into silicon to a depth of ≈65 nm. The line edge roughness (3σ) was evaluated to be less than 3 nm both in the transfer layer and in silicon. The authors also demonstrate that a similar three-layer stack can be used for metal lift-off of high resolution patterns. A device application is demonstrated by fabricating 50 nm half pitch dense nickel contacts to an InAs nanowire.

Networks of neurons cultured on-chip can provide insights into both normal and disease-state brain function. The ability to guide neuronal growth in specific, artificially designed patterns allows us to study how brain function follows form. Primary cortical cells cultured on nanograting scaffolds, in particular astrocytes, showed highly ordered regions of dendritic outgrowth. Usually, materials suitable for nanopatterning have a stiffness far above that of the extracellular matrix. In this paper, the authors studied two materials with large differences in stiffness, polydimethylsiloxane(PDMS) and silicon. Our results show that both nanopatterned silicon and PDMS guide the outgrowth of astrocytes in cortical cell culture, but the growth of the astrocyte is affected by the stiffness of the substrate, as revealed by differences in the cell soma size and the organization of the outgrowth.

Molybdenum disulfide (MoS2) two-dimensional nanostructures have been actively explored for ultrasmall transistors beyond graphene. The current prevailing methods for producing MoS2devices involve multiple wet chemistry steps, which not only are time consuming, but may also unfavorably affect material quality and impair device performance through the chemical processes. Here, the authors report the first dry-transferred pristine MoS2field-effect transistors(FETs) without any post-transfer lithographical and chemical processes, by using a facile, completely dry transfer technique with high throughput and high precision in alignment. The authors also show that the device performance can be greatly boosted by thermal annealing. Combining the dry-transfer technique with thermal annealing, the authors achieve MoS2FETs with mobility up to 76 cm2/(V s) and on/off ratios exceeding 107. The authors further show how continued annealing cycles improve the MoS2devices' conductance, mobility, on/off ratio, transconductance, threshold voltage, and contact quality.

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The authors report on the first experimental characterization of a fiber tip-based electron source, where electron emission can be triggered by both electric field and optical excitation. Our approach consists of coating the open aperture of a commercial 100 nm apex size near-field scanning optical microscopy fiber tip with a 10 nm thick tungsten (W) layer, which is back-illuminated by a 405 nm continuous-wave laser beam in the presence of an extraction electric field. Despite the very low optical transmission of the fiber due to the subwavelength aperture size, measurements show a clearly enhanced emission when photoexciting the W layer with respect to pure field emission. The emission response time is slower than the optical trigger time, suggesting that thermal effects are predominant in the studied regime. To back up this hypothesis, the authors fabricated a nanometric thermocouple probe based on a Pt/Au junction and measured the temporal response of the tip temperature. The measured switch-on time for the tip temperature is consistent with the switch-on time of the optically enhanced electron emission.

To clarify the origin of the superior field emission characteristics of carbon-coated emitters, the authors investigated the field enhancement and the work function of model systems calculated by numerical simulations. They propose that the field enhancement is due to the triple junctions, which are distributed on the surface of the carbon film consisting of sp3 (diamond-like) insulating and sp2 (graphite-like) conducting nanometer-sized grains. The electric field around the triple junction is one order of magnitude higher than at other places. Based on ab initiodensity functional theory calculations, the authors found that (1) the work functions of diamond and graphite dramatically decrease down to 3–3.6 eV upon hydrogen termination, and (2) the effective work functions of these models decrease to 2–2.5 eV by applying an external electric field of 2.57 × 107 V/cm. They also estimated the field emissioncurrent from the potential distribution and the local density of states under the external electric field applied. As a result, the authors found that hydrogen termination significantly increases the field emissioncurrent. The results suggest that the triple junction and hydrogen termination are promising candidates as the mechanism of improving the emission of the carbon-coated emitters.

The paper concerns the problems associated with the generation and measurement of vacuum in small-volume microelectromechanical(MEMS)devices. A concept of equipping vacuumMEMS with miniature vacuum pump and gauge has been presented. The ion-sorption vacuum micropump developed by the authors has been integrated with two “external” miniature pressure sensors: a specially developed miniature Bayard-Alpert gauge and a MEMS-type Pirani sensor. The pressure during the pumping process was in-situmeasured and co-work of vacuum micropump and sensors has been investigated. The experimental results confirmed good pumping properties of the micropump, but indicated that the work of micropump significantly affects the operation of vacuum sensors and vice versa.

The authors have built up a dedicated ultrahigh vacuum setup to measure ultraviolet (266 nm photons) photoemission properties of nanocrystalline diamond thin films obtained by chemical vapor deposition on silicon substrates. The authors validated their setup by measuring polycrystalline copper quantum efficiency of ∼10−6, which is in good agreement with literature. The authors also measured quantum efficiency of bare silicon (highly p and n doped) and demonstrate strong influence of doping type. The authors then measured quantum efficiency of silicon samples coated with submicron (50 and 100 nm thick) nanocrystalline diamond layers. This coating reveals to have major influence on the photoemission properties when deposited on highly n-doped silicon samples. The authors obtain quantum yield as high as 1.60 × 10−5. The relatively high quantum efficiency of such structure associated with its high stability in air and easy processing make it a good candidate as fast electron source for electron gun based systems such as scanning/transmission electron microscopes or x-ray sources.

This paper describes changes observed in the emission from a 100-tip Spindt cathode array operated at emission levels that produced tip self-heating and resulting temperatures sufficient to cause surfaceself-diffusion. This is the well-known thermal-field-forming effect that can produce smoothing and blunting—or buildup and sharpening—of the emitter tips, depending on whether the surface energy or the electrostatic field energy dominates. Although a greater than 50% decrease in emission current for a set voltage was observed, Fowler/Nordheim analysis of the emission data produced the unexpected result that the field-voltage proportionality factor had increased and the emitting area had decreased.

A method for studying fluctuations in the microscopic emission parameters of flat multiple-point cathodes has been developed. For field emitters based on polymer/multiwalled carbon nanotubenanocomposites, the statistical distribution of the effective heights of emission centers has been obtained. Numerical estimates made using Pearson's chi-squared test confirmed that this distribution is lognormal. For these field emitters, the influence of the emission current on the statistical parameters that describe the emission characteristics is discussed.